EP0039791B1 - Method of producing sinterable titanium base alloy powder - Google Patents

Abstract

A process is disclosed for the preparation of alloy powders, which can be sintered and which are based on titanium, by the calciothermal reduction of the oxides of the metals forming the alloys in the presence of neutral additives. This can be accomplished by mixing TiO2 with oxides of the other components of the alloy, admixing an alkaline earth oxide or carbonate with the metal oxides, calcining the mixture. After cooling, the mixture is crushed and calcium is added. Thereafter, green compacts are formed which are heated and leached to remove the calcium oxide. The powder obtained is of uniform structure composition, is free of segrations of oxides nitrides carbides and/or hydrides and has high bulk and tap densities and can be molded by isostatic hot molding.

Description

The invention relates to a method for producing sinterable alloy powders based on titanium by calciothermal reduction of the oxides of the metals forming the alloys in the presence of indifferent additives.

Titanium and titanium-based alloys have found many applications due to their special material properties. Due to the relatively complex manufacturing processes, the alloys of titanium in particular are relatively expensive.

To produce titanium, the naturally occurring oxide is reduced with coal in the presence of chlorine and titanium tetrachloride is obtained, which is processed into the titanium sponge by reduction with metallic sodium or magnesium. The titanium sponge is then, after adding the other alloy components such. As aluminum and vanadium, melted and cast or rolled into bars, profiles or sheets. The near-contour shaped parts are given their final shape by machining. A disadvantage of this procedure is the sometimes considerable amount of machined alloy. It is therefore not readily possible to produce complicated shaped parts in this way at reasonable prices.

The production of such molded parts is more successful using powder metallurgy. In particular, two processes have become known for the production of the alloy powder. One method is characterized in that the titanium sponge is fused together with alloy partners to form a rod-shaped electrode. The electrode is atomized into powder rotating under the action of a plasma flame and at high speeds, although as a rule the powder obtained must be subjected to additional comminution (grinding) because of the formation of agglomerates. However, this REP process is extremely complex, in particular due to the apparatus costs, and is also limited to a certain electrode size with regard to the batch weight.

The second way known for the preparation of the powder consists in hydrogenating the titanium sponge, grinding the brittle titanium hydride, adding the other alloying partners in powder form, intimately grinding, dehydrating at elevated temperatures in vacuo and the powder obtained in a manner known per se pressed and sintered. This process is also complex and cannot satisfy the process.

The invention is therefore based on the object of finding a method for producing sinterable alloy powders based on titanium which does not have these disadvantages. The alloy powders must have a certain grain size and grain size distribution in order to achieve a sufficient bulk density and tapping density. The alloy powders should be uniform, i. that is, each powder particle must have the same composition and structure as the other alloy particles. The alloy powders must also be free from precipitates of oxides, nitrides, carbides and hydrides, since otherwise the sinterability is not ensured. It is only the sum of the aforementioned properties that makes an alloy powder possible for the production of molded parts by pressing and sintering. It should therefore be possible to subject the powders to hot isostatic pressing, which means that it is possible to manufacture near-contour components without complex post-processing.

The invention is particularly based on the object of producing alloy powders of such uniformity and purity that they are suitable in the aircraft industry for the production of mechanically highly stressable parts.

DE-PS 935456 discloses a process for obtaining alloy powders, preferably suitable for the production of sintered bodies, by reducing metal compounds and, if appropriate, subsequently extracting by-products, which is characterized in that intimate mixtures of such metal compounds, at least one of which is difficult to reduce, with metals; such as sodium, calcium, can be reduced. An embodiment of the process is characterized in that the reduction takes place in the presence of indifferent, refractory, easily removable substances.

The co-reduction of oxides of titanium, copper and tungsten and other oxides is thus described in this patent. In practice, however, the process has found no entry, since no sinterable powders which are homogeneous in their composition and structure could be obtained by this procedure. However, the process described in that patent appeared to have been a potentially appropriate step in the right direction. The method according to the invention is therefore based on this prior art.

• a) Titanoxid mit den Oxiden der anderen Legierungsbestandteile in, bezogen auf Metalle, den der gewünschten Legierung entsprechenden Mengen versetzt, Erdalkalioxid oder Erdalkalicarbonat in einem Molverhältnis von zu reduzierenden Metall- oxiden zur Erdalkalioxid oder Erdalkalicarbonat von 1 : 1 bis 6 : 1 zugibt, das Gemisch homogenisiert, bei Temperaturen von 1000 bis 1300° C 6 bis 18 h glüht, abkühlt und auf eine Teilchengröße _^<_ 1 mm zerkleinert,
• b) kleinstückiges Calcium in einer, bezogen auf Sauerstoffgehalt der zu reduzierenden Oxide, 1,2- bis 2,0fachen äquivalenten Menge, sowie einen Booster in einem Molverhältnis von zu reduzierenden Oxiden zu Booster von 1 : 0,01 bis 1 : 0,2 zugibt, diesen Reaktionsansatz vermischt, die Mischung zu Grünlingen verpreßt und in einen Reaktionstiegel einfüllt und verschließt,
• c) den Reaktionstiegel in einen evakuierbaren und beheizbaren Reaktionsofen eingibt, den Reaktionstiegel auf einen Anfangsdruck von 10 bis 10-¹ Pa evakuiert und auf eine Temperatur von 1000 bis 1300°C für eine Dauer von 2 bis 8 h aufheizt, sodann abkühlt und
• d) den Reaktionstiegel aus dem Reaktionsofen entnimmt, das Reaktionsprodukt aus dem Reaktionstiegel entfernt und auf eine Korngröße ≦2 mm zerkleinert, sodann das Calciumoxid mit einem geeigneten Lösemittel, welches das Legierungspulver nicht löst, auslaugt und das erhaltene Legierungspulver auswäscht und trocknet.

Surprisingly, it has now been found that the problems mentioned at the outset can be achieved by a process which is characterized in that

• a) titanium oxide with the oxides of the other alloy constituents in, based on metals, the amounts corresponding to the desired alloy are added, alkaline earth oxide or alkaline earth carbonate in a molar ratio of metal to be reduced add oxides to alkaline earth or alkaline earth carbonate from 1: 1 to 6: 1, homogenize the mixture, glow at temperatures from 1000 to 1300 ° C for 6 to 18 h, cool and shred to a particle size _ ^<_ 1 mm,
• b) small-scale calcium in an amount, based on the oxygen content of the oxides to be reduced, of 1.2 to 2.0 times the equivalent amount, and a booster in a molar ratio of oxides to be reduced to boosters of 1: 0.01 to 1: 0.2 admits, mixes this reaction batch, compresses the mixture into green compacts and fills it in a reaction crucible and seals it,
• c) the reaction crucible is placed in an evacuable and heatable reaction furnace, the reaction crucible is evacuated to an initial pressure of 10 to 10 ¹ Pa and heated to a temperature of 1000 to 1300 ° C. for a period of 2 to 8 h, then cooled and
• d) the reaction crucible is removed from the reaction furnace, the reaction product is removed from the reaction crucible and comminuted to a particle size ≦ 2 mm, then the calcium oxide is leached out with a suitable solvent which does not dissolve the alloy powder, and the alloy powder obtained is washed out and dried.

The process according to the invention is thus characterized by a combination of special process measures.

According to the aforementioned method according to the invention, the oxides of the alloy partners, based on metal, are initially provided in the amounts corresponding to the desired alloy composition, in accordance with the desired alloy. It has been shown in many experiments that direct reduction of these mixtures of the oxides does not produce any sinterable alloy powders, regardless of the pretreatment. Metal powders are formed, some of which may consist of the desired alloy, but may also consist of pure titanium or of the metals or alloys of the other reactants in uncontrollable amounts. It also contains particles which contain titanium as a base and the other metal components alloyed in different amounts.

These difficulties can surprisingly be overcome by adding certain amounts of alkaline earth oxide or alkaline earth carbonate to the mixtures of the metal oxides to be reduced and burning them up to form an oxidic multi-substance system, the number of phases of which is smaller than the sum of the starting components (hereinafter referred to as mixed oxide).

According to the invention, the molar ratio of the metal oxides to be reduced to alkaline earth oxide or alkaline earth carbonate is 1: 1 to 6: 1, a range from 1.2: 1 to 2: 1 is preferred. Calcium oxide or calcium carbonate is preferably used as the alkaline earth oxide or carbonate.

In contrast to the teaching of DE-PS 935456 cited in the prior art, the alkaline earth oxide, that is to say preferably the calcium oxide, is not added as a desensitizing agent, but rather serves to produce a mixed oxide in which the mixture of the metal oxides to be reduced with the alkaline earth oxide or alkaline earth carbonate after homogenization at temperatures of 1000 to 1300 ° C, in particular 1200 to 1280 ° C, 6 to 18 h, preferably 8 to 12 h, is annealed. A mixed oxide with a reduced number of phases is formed which, after comminution to a particle size of approximately ≦ 1 mm, has the same gross composition.

It is particularly advantageous to use alkaline earth carbonate, in particular calcium carbonate, instead of alkaline earth oxide. In the annealing process for producing the mixed oxide, z. B. from the calcium carbonate carbon dioxide. Calcium oxide forms with a fresh and active surface. At the same time, the annealed mixed oxide is loosened and can be shredded more easily. The crushing of the annealing product succeeds in a simple manner, for. B. using jaw crushers and subsequent grinding with a cone mill.

In the second process step, the annealed mixed oxide thus obtained is mixed with small-scale calcium. The calcium should in particular have a particle size of 0.5 to 8 mm, preferably 2 to 3 mm. The amount of calcium is related to the oxygen content of the oxides to be reduced. Based on the oxygen content of the oxides to be reduced, 1.2 to 2.0 times, preferably 1.3 to 1.6 times, the equivalent amount of calcium is used. So you need z. B. per mole of Ti0 ₂ 2.4 to 3.6 moles of Ca, per mole of A1 ₂ 0 ₃ 3.6 to 5.4 moles of Ca, per mole of V ₂ 0 ₅ 6.0 to 9.0 moles of Ca.

The addition of a booster to the reaction mixture is of particular importance. In metallothermal energy, a booster is a compound that reacts with strong exothermic heat in the metallothermic reduction. Examples of such boosters are oxygen-rich compounds, such as. B. calcium peroxide, sodium chlorate, sodium peroxide, potassium perchlorate. When selecting the boosters, care must be taken to ensure that no compounds are introduced which would interfere with the alloy formation as an undesired alloy partner. In the method according to the invention, potassium perchlorate has proven itself in a particular way as a booster. A strong exothermic reaction occurs when potassium perchlorate is reacted with calcium. In addition, potassium perchlorate is relatively cheap. A particular advantage of potassium perchlorate is that it is available anhydrous and is not hygroscopic.

The teaching according to the invention in the calciothermal coreduction to a booster use, is in direct contrast to the teaching of DE-PS 935 456. There the opinion is held that the reduction would take place with such strong heat that the resulting alloy melt or powder would be very coarse. DE-PS 935456 therefore teaches to add indifferent, refractory compounds, in particular oxides, to the reaction mixture in such cases. However, the addition of a booster in the process according to the invention leads to alloy powders in which the individual particles each have the same composition and have the shape required to achieve a necessary high knocking and bulk density.

The molar ratio of oxides to boosters to be reduced is 1: 0.01 to 1: 0.2, preferably 1 0.03 to 1: 0.13. The reaction mixture consisting of oxides, calcium and boosters is now mixed thoroughly.

It is possible to add one or more of the desired alloy powders in the form of a metal powder having a particle size Metall 40 11 m to the reaction mixture in stage b). However, due to the problems of a uniform distribution of the added metal powder in the oxide mixture, this is particularly recommended only if the corresponding oxide of the metal sublimates at relatively low temperatures and therefore cannot be annealed together with the other oxides in step a) without loss. An example of such a metal is molybdenum. Molybdenum trioxide sublimes at temperatures> 760 ° C and is expediently added in step b) in the form of a fine metal powder. The mixture is pressed into green compacts. These green compacts are filled into a reaction crucible. It has been shown that a good degree of filling can be achieved, a uniform reaction can be achieved by suitable heat transport and, at the same time, the reduced reaction material can be removed from the crucible without problems if green compacts with a cylindrical shape are used. The green compacts should have a diameter of approximately 50 mm and a height of 30 mm. Deviations from this dimensioning are of course possible.

The green compacts are now filled into a reaction crucible. A reaction crucible is used which is chemically and mechanically stable under the given conditions. Crucibles made from titanium sheets have proven particularly useful.

In the third process step, the reaction crucible is now closed, with a low lumen socket in the closure cover, through which the crucible can be evacuated. The reaction crucible is placed in a heatable reaction furnace and evacuated to an initial pressure of approximately 10 to 10 ¹ Pa. The reaction crucible is now heated to a temperature of 1000 to 1300 ° C. Some calcium distils into the suction nozzle, condenses there and closes the nozzle. Such a self-closing crucible is known for example from DE-AS 1 124 248. A pressure is then set in the reaction crucible which corresponds to the pressure of the calcium at the given temperature. The calcium which is removed from the equilibrium during the reaction and is bound as an oxide can be neglected, since the replication of the gaseous calcium takes place faster than the path reaction. The reaction crucible is left at the reaction temperature for 2 to 8, preferably 2 to 6 h.

In a special embodiment of the method according to the invention, the gaseous potassium formed during the reduction of the potassium perchlorate used as a booster and which passes through the evacuation port before the reaction vessel is sealed by condensing calcium is absorbed in an intermediate vessel which is filled with silica gel.

Surprisingly, it has been shown that the gaseous potassium is absorbed by the silica gel in a form that the potassium-laden silica gel can be safely handled in the air. If you put the silica gel so loaded in water, hydrogen evolves slowly and over a long period of time, so that the metallic potassium can be safely collected and removed in this way.

The booster, especially potassium perchlorate, is reduced during the reaction period. In addition to metallic potassium, calcium oxide and calcium chloride are formed. The heat released in this way favors and accelerates the reduction of the metal oxides. The desired alloy formation occurs during and after the reduction. The melting temperature of the alloy, which is surrounded on all sides by calcium oxide, is briefly exceeded. Supported by the molten calcium chloride and under the influence of the surface tension, the alloy particles form in the desired shape of an approximate spherical shape.

In the last stage of the process, the reaction crucible is now removed from the furnace, the crucible is opened, the reaction product is removed from the crucible and comminuted to a particle size of <2 mm. The calcium oxide is mixed with a suitable solvent, especially dilute acids, e.g. B. dilute acetic acid or dilute hydrochloric acid or complexing agents, such as ethylenediaminetetraacetic acid, leached. The remaining alloy powder is washed neutral and dried.

• der Stufe a):
  • Abkühlen der geglühten Oxidmischung, Zerkleinern der geglühten Oxidmischung,
• der Stufe b):
  • Mischen des Reaktionsgemisches, Verpressen des Reaktionsgemisches zu Grünlingen, Einfüllen der Grünlinge in den Reaktionstiegel,
• der Stufe c):
  • Einbringen des Reaktionstiegels in den heizbaren Ofen,
• der Stufe d):
  • Entnehmen des Reaktionstiegels aus dem Reaktionsofen, Entfernen des Reaktionsproduktes aus dem Reaktionstiegel, Zerkleinern, Auslaugen, Trocknen des Reaktionsproduktes.

It has proven to be advantageous to carry out one or more of the process steps under a protective gas atmosphere. Argon in particular is used as the protective gas. A particularly preferred embodiment of the process according to the invention is therefore characterized in that one or more process steps are carried out under a protective gas atmosphere, in particular one or more of the process steps

• level a):
  • Cooling the annealed oxide mixture, comminuting the annealed oxide mixture,
• level b):
  • Mixing the reaction mixture, pressing the reaction mixture into green compacts, filling the green compacts into the reaction crucible,
• level c):
  • Placing the reaction crucible in the heatable furnace,
• level d):
  • Removal of the reaction crucible from the reaction furnace, removal of the reaction product from the reaction crucible, comminution, leaching, drying of the reaction product.

Contains the in process step c) resulting reduced reaction product is hydrogen in an unacceptable amount, it is recommended that the reduction product to a vacuum treatment at 10 to 10- ² Pa at a temperature of 600 to 1000 ° C, in particular 800 to 900 ° C, for a time from 1 to 8 h, preferably 2 to 3 h.

Due to its particle size and particle size distribution, the alloy powder obtained according to the invention has the required tap density of approximately ≧ 60% of the theoretical density. Knock densities of up to almost 70% of theory are achieved. The examination of the alloy powders by microscopic micrographs and with the microsensor prove a uniform composition of each of the alloy particles. They are free of excretions which impair the sinterability or would reduce the mechanical strength of the molded bodies obtained by hot isostatic pressing.

With the method according to the invention, the standard alloys examined with regard to their properties, such as, for. B. TiA16V4; TiAl6V6Sn2; TiAl4Mo4Sn2; TiAl6Zr5Mo0.5Si0.25; TiA12V11.5Zr11Sn2; TiA13V10Fe3; manufacture flawlessly.

The particular advantages of the process according to the invention additionally consist in the fact that the raw materials, namely the oxides of the metals, are available in practically unlimited quantities. Apart from their cleaning, they do not require any special processing. By choosing the type and amount of the metal oxides to be reduced, the alloys in the desired composition can easily be produced. The yields in the process according to the invention are very high (> 96%) since no loss-making intermediate steps, as in the process of the prior art, are required. The method according to the invention is therefore particularly inexpensive. The expenditure on equipment is kept to a minimum. The reproducibility of the alloys produced according to the process is great. The sinterable alloy powders can be produced directly from purified raw materials occurring in nature, avoiding remelting processes.

The process according to the invention is explained in more detail with reference to the following examples.

example 1 Production of a TiAl6V4 alloy

1377.10 g TiO ₂ , 85.63 g Al ₂ O ₃ , 65.60 g V ₂ O ₅ and 1601.20 g CaCO ₃ are mixed homogeneously and annealed at 1100 ° C. for 12 hours. The annealed mixed oxide is crushed to a grain size of <1 mm using a jaw crusher and a cone mill and has the following grain distribution curve: (w / o = weight percent)

The bulk density is approx. 1.40 g / cm ³ and the tap density is approx. 2.30 g / cm ³ . After annealing, the yield of mixed oxide phases amounts to 2418.0 g ≅ 99.7%.

1000 g of this mixed oxide are mixed homogeneously with 1070.6 g Ca and 91.40 g KClO ₄ (≅0.08 mol KClO ₄ / mol alloy powder) and green parts with the dimensions of 50 mm diameter and 30 mm height are produced therefrom. These green compacts are then reduced in a titanium crucible for 8 hours at a temperature of 1150 ° C. and at an initial pressure of 1 Pa. After reduction to a particle size of <2 mm, the reaction product is leached out with dilute hydrochloric acid, the alloy powder obtained is vacuum-treated and dried. The yield of alloy powder is approx. 361.0 g = 95.6%, based on the theoretical yield.

The alloy powder obtained has a bulk density of 1.96 g / cm ³ ≅44.95% and a tap density of 2.56 g / cm ³ ≅58.6% of the theoretical density.

The grain distribution curve has the following composition:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the alloy powder shows that structurally homogeneous alloy particles are present, the structure formation being classified as lamellar to fine-globular. A homogeneous distribution between a high α and a low β content can be seen in the alloy.

Example 2 Production of a TiAl6V4 alloy

For a second alloy, 1377.10 g Ti0 ₂ , 85.63 g A1 ₂ 0 ₃ , 65.60 g V ₂ 0 ₅ and 644.9 g MgO are mixed homogeneously and annealed at 1250 ° C. for about 12 hours and that annealed oxide obtained treated as in Example 1.

After comminution, the mixed oxide has the following particle size distribution:

The bulk density of the comminuted mixed oxide is approximately 1.33 g / cm3, the tap density is approximately 1.97 g / cm ³ . After annealing, the mixed oxide is obtained with a yield of 2154.9 g≅99.16%.

895 g of the mixed oxide are intimately mixed with 1290 g Ca and 133 g KClO ₄ (≅0.12 mol KClO ₄ / mol alloy powder), annealed at 1100 ° C for 12 h and treated as in Example 1.

The yield of titanium alloy powder is 365.5 g, which corresponds to 96.75% of the theoretically possible yield. The alloy powder has a bulk density of 2.14 g / cm ³ ≅48.97% and a tap density of 2.78 g / cm ³ ≅63.76%, based on the theoretical density.

The grain distribution curve of the alloy powder has the following composition:

The chemical analysis shows the following composition:

It can be seen from the results of the metallographic examination that the alloy particles have the same structure, which can largely be characterized as lamellar to fine globular. The microstructure also shows that the alloy particles have a homogeneous α and β phase distribution.

Example 3 Production of a TiAl6V6Sn2 alloy

• 25 - 32 µm = 8,0 w/o
• < 25 µm = 13,8 w/o

1334.40 g TiO ₂ , 103.90 g Al ₂ O ₃ , 99.3 g V ₂ O ₅ , 45.15 g SnO and 1601.2 g CaCO ₃ are mixed intimately or homogeneously and about 12 hours at 1250 ° C annealed. The annealed oxide is crushed to a grain size of <1 mm≅1000 µm using a jaw crusher and a cone mill and has the following grain distribution curve:

• 25 - 32 µm = 8.0 w / o
• <25 µm = 13.8 w / o

The bulk density of the comminuted oxide is 1.63 g / cm ³ and the tap density is 2.58 g / cm ³ . After the annealing, the mixed oxide is obtained with a yield of 2415.0 g ≅97.4%.

1000 g of this mixed oxide are mixed homogeneously with 1133.9 g Ca and 129.8 g KCI0 ₄ (0.12 mol KCI0 _{4 /} mol alloy powder), compacted, reduced at 1150 ° C. for 8 hours and, as described in Example 1, processed further. The yield of titanium alloy powder is 367.2 g, which corresponds to 96.5%, based on the theoretical yield.

The alloy powder has a bulk density of 2.18 g / cm ³ ≅49.3% and a tap density of 2.81 g / cm ³ ≅63.45% of the theoretical density.

The grain distribution curve of the alloy powder has the following composition:

The chemical analysis shows the following composition:

The metallographic examination shows alloy particles with a homogeneous structure and phase distribution. The structure shows fine-lamellar structure of the α phase, which is stabilized by the addition of tin. There are no Ti ₃ Al phases that hinder the non-cutting shaping.

Example 4 Production of a TiAl4Mo4Sn2 alloy

1439.5 g TiO ₂ , 72.5 g Al ₂ O ₃ , 21.8 g SnO and 1601.2 g CaC0 ₃ are mixed homogeneously and annealed at 1250 ° C for approx. 12 h, then the annealed mixed oxide is passed through a Jaw crusher and a cone mill crushed to a grain size of <1 mm. The mixed oxide has the following grain distribution curve:

The bulk density of the mixed oxide is 1.84 g / cm3 and the tap density is 2.76 g / cm ³ . The yield of usable mixed oxide is 2358.0 g ≅ 98.1% of the theoretical yield.

1000 g of this mixed oxide are mixed homogeneously with 24.90 g Mo powder, 1109.1 g Ca and 115.3 g KClO ₄ , compacted and, as described in Example 1, further treated. The yield of titanium alloy powder is 384.8 g ≅ 96.5% of the theoretical yield.

The alloy powder has a bulk density of 2.39 g / cm ³ ≅52.8% and a tap density of 2.88 g / cm ³ ≅63.6% of the theoretical density.

The grain distribution curve has the following composition:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination shows alloy particles with a homogeneous structure. In addition to the stabilized α phase as the main there is a small amount of ß in the alloy particles.

Example 5 Making one TiAl6Zr5Mo0.5Si0.25 alloy

1379.9 g TiO ₂ , 106.3 g Al ₂ O ₃ , 63.3 g ZrO ₂ , 10.7 g SiO ₂ and 1601.2 g CaC0 ₃ are mixed homogeneously and annealed at 1250 ° C. for 12 hours. The annealed mixed oxide is then crushed to a grain size of <1 mm ≅ 1000 µm using a jaw crusher and a cone mill. The grain distribution curve has the following composition:

The bulk density of the mixed oxide is 2.12 g / cm ³ ≅48.11% and the tap density is 2.54 g / cm ³ ≅57.65% of the theoretical density. The yield of usable mixed oxide is 2425.0 g and corresponds to 98.7% of the theoretical yield.

1000 g of this mixed oxide are mixed homogeneously with 1.91 g of very fine-grained molybdenum metal powder, 1125.9 g of Ca and 131.2 g of KCI0 ₄ (0.12 mol of KClO ₄ / mol of alloy powder) and, as described in Example 1, processed further. The yield of titanium alloy powder is 369.4g≅96.69% based on the theoretical yield of alloy powder.

The alloy powder has a bulk density of 2.12 g / cm ³ ≅48.11% and a tap density of 2.68 g / cm ³ ≅60.9% of the theoretical density.

The alloy powder has the following grain distribution curve:

The chemical analysis of the alloy powder shows the following composition:

Metallographic studies show that structurally homogeneous alloy particles are present, with a pronounced, β-stabilized microstructure which, as is known, gives this alloy higher heat strengths after sintering.

Example 6 Making one TiA12V11,5Zr11 Sn2 alloy

1245.22 g TiO ₂ , 38.0 g Al ₂ O ₃ , 207.5 g V ₂ O ₅ , 149.4 g ZrO ₂ , 23.1 g SnO and 1601.2 g CaCO ₃ are mixed intimately or homogeneously and annealed at 1250 ° C for 12 hours. The annealed mixed oxide is crushed to a grain size of <mm≅1000 µm using a jaw crusher and a cone mill and then has the following grain distribution curve:

The bulk density of the annealed mixed oxide is 2.415 g / cm ³ ≅50.15% and the tap density 3.185 g / cm ³ ≅66.2% of the theoretical density. The yield of usable mixed oxides is 2412.2 g, which is 94.2% of the theoretical yield.

1000 g of this mixed oxide are mixed homogeneously with 1640.2 g Ca and 162.3 g KCI0 ₄ (0.10 mol KCI0 ₄ / mol alloy powder) and, as described in Example 1, processed further. The yield of alloy powder is 378.2 g≅95.55% of the theoretical yield.

The alloy powder has a bulk density of 2.68 g / cm ³ ≅55.65% and a tap density of 3.13 g / cm ³ ≅65.1% of the theoretical density.

The alloy powder has the following grain size division curve on:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the alloy powder shows particles with a homogeneous structure and β stabilization. Sintered parts made from these alloys result in components with relatively high fracture toughness.

Example 7 Production of a TiAl3V10Fe3 alloy

1325.2 g TiO ₂ , 55.2 g Al ₂ O ₃ . 168.6 g V ₂ O ₅ , 39.4 g Fe ₃ 0 ₄ and 1601.2 g CaCO ₃ are mixed homogeneously and annealed at a temperature of 1100 ° C for 12 h. The annealed mixed oxide is then crushed to a grain size of <1 mm ≅ 1000 µm using a jaw crusher and a cone mill. The grain distribution curve then has the following composition:

The bulk density of the annealed mixed oxide is 2.314 g / cm ³ ≅49.61% and the tap density 3.012 g / cm ³ s64.6% of the theoretical density. The yield of usable mixed oxides is 2398.6 gs 96.5% of the theoretical yield.

1000 g of this mixed oxide are mixed homogeneously with 2833.8 g Ca and 147.95 g KClO ₄ (0.12 mol KCI0 _{4 /} mol alloy powder) and processed as described in Example 1. The yield of alloy powder is 360.8 g ≅94.8% of the theoretical yield.

The alloy powder has a bulk density of 2.410 g / cm ³ ≅51.7% and a tap density of 2.981 g / cm ³ ≅63.9% of the theoretical density.

The measurement of the grain distribution curve of the alloy powder gives the following values:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the powdery alloy shows particles with a homogeneous structure and a stabilized α phase. Sintered parts made from these alloy powders are said to have a higher creep resistance.

From the examples it can be seen that the alloy powders produced by the process according to the invention contain a typical process content of 0.05 to 0.15% by weight calcium. However, this amount has no influence on the quality and processability of the alloy powder.

Example 8 Production of a TiAl6V4 alloy

1377.10 g TiO ₂ , 85.63 g Al ₂ O ₃ , 65.60 g V ₂ O ₅ and 1034.52 g Ca0 (1: 1) are mixed homogeneously and annealed at 1000 ° C for 18 hours. The annealed mixed oxide is cone and jaw crushers

Cross beater mill crushed to a grain size of <1 mm and has the following grain distribution curve:

The bulk density is approximately 1.45 g / cm ³ . The tap density is 2.28 g / cm ³ . After annealing, the yield amounts to 2605.8 g ≅ 98.7%.

1000 g of this mixed oxide are mixed homogeneously with 1051.62 g Ca (1: 1.2 mol) and 228.50 g KClO ₄ (≅0.20 mol KClO ₄ / mol alloy powder) and green bodies with the dimensions of 50 mm diameter and a height of 30 mm.

These green compacts are then introduced into the reaction crucible, the reaction crucible is inserted into the furnace and the furnace is closed. The reaction chamber with reduction crucible is evacuated to a pressure of <10 Pa at room temperature and then heated to 1300 ° C. and held at this temperature for 2 hours.

After the reduction, the reaction product is comminuted to a maximum particle size of <2 mm, the comminuted reaction product is leached with dilute nitric acid, filtered and washed until neutral. The alloy powder obtained is vacuum-treated and dried. The yield of alloy powder is 363.5g≅94.8%, based on the theoretical yield.

The alloy powder obtained has a bulk density of 2.03 g / cm ³ ≅46.56% and a tap density of 2.69 g / cm ³ ≅61.7% of the theoretical density.

The grain distribution curve of the alloy powder has the following composition:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the alloy powder shows that there are structurally homogeneous alloy particles with uniform α and β distribution. The α proportion in the alloy particles predominates. The development of the individual phases can be classified as fine globular to lamellar.

Example 9 Production of a TiAl6V4 alloy

1377.10 g TiO ₂ , 85.63 g Al ₂ O ₃ , 65.60 g V ₂ O ₅ and 172.45 g Ca0 are mixed homogeneously with one another (6: 1) and annealed at 1300 ° C. for 6 hours.

The annealed mixed oxide is crushed to a grain size of <1 mm using a jaw crusher, cone and cross beater mill and has the following grain distribution curve:

The bulk density of the annealed, mixed oxide phases is 1.58 g / cm ³ and the tap density is approximately 2.48 g / cm ³ . After annealing, the yield is 1665.7 g ≅97.9%, based on the theoretical yield.

1000 g of this mixed oxide are mixed homogeneously with 1991.80 g Ca and 11.43 g KClO ₄ (≅0.01 mol KClO ₄ / mol alloy powder) and green parts with the dimensions of 50 mm diameter and 30 mm height are produced therefrom.

The green compacts are then inserted into the reaction crucible, the reaction crucible is placed in the furnace and the furnace is then closed. The reaction chamber with the reduction crucible is then evacuated to a pressure of 10- ¹ Pa at room temperature and then heated up to 1000 ° C. and held at this temperature for 8 hours.

After the reduction, the reaction product is crushed to a grain size <2 mm, then leached with formic acid, vacuum treated and dried. The yield of alloy powder is approx. 358 g≅93.5%, based on the theoretical yield.

The alloy powder obtained has a bulk density of 1.91 g / cm ³ ≅43.80% and a tap density of 2.76 g / cm ³ ≅63.6% of the theoretical density.

The grain distribution curve has the following composition:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the alloy powder shows that structurally homogeneous alloy particles are present, the microstructure being lamellar to fine-globular. The alloy mainly consists of a high proportion of α and a low proportion of β.

Example 10 Production of a TiAl3V1 OFe3 alloy

1325.2 g TiO ₂ , 55.2 g Al ₂ O ₃ , 168.6 g V ₂ O ₅ , 39.4 g Fe ₃ 0 ₄ and 260.1 g Ca0 (4: 1) are mixed homogeneously and at 1300 ° C annealed for 10 h.

The annealed mixed oxide is crushed to a grain size of <1 mm using a jaw crusher, cone and cross beater mill and has the following grain distribution curve:

The bulk density of the mixed oxide is 1.54 g / cm ³ and the tap density is 2.49 g / cm ³ . After annealing, the yield is 1869.6 g -99.7% of the theoretical yield. 1000 g of this mixed oxide are mixed homogeneously with 598.8 g Ca (1: 1.5) and 128.5 g KClO ₄ (≅0.05 mol KCI0 _{4 /} mol alloy powder) and green parts with the dimensions of 50 mm height and 30 mm diameter made from it.

These green compacts are then introduced into the reaction crucible and then the reaction crucible is charged into the furnace and evacuated to a pressure of 10 ^-1 Pa at room temperature and then heated up to 1200 ° C. The response time is 6 hours.

After the reduction, the reaction product is crushed to a maximum grain size of <2 mm, then leached with dilute hydrochloric acid, vacuum-treated and dried. The yield of alloy powder is 501.8 g ≅ 97.4%, based on the theoretical yield.

The alloy powder produced has a bulk density of 2.43 g / cm ³ ≅53.3% and a tap density of 2.978 g / cm ³ ≅65.2% of the theoretical density.

The measurement of the grain distribution curve of the alloy powder gives the following values:

The chemical analysis of the alloy powder shows the following composition:

The metallographic examination of the alloy powder shows particles with a homogeneous structure and a stabilized α phase.

Claims (9)

1. Process for the production of sinterable titaniumbased alloy powders, by calcio-thermic reduction of the oxides of the metals forming the alloys, in the presence of inert additives, characterised in that

a) the oxides of the other alloy-constituents are added to titanium oxide, in amounts which, referred to metals, correspond to the desired alloy, the oxide, or carbonate, of an alkaline earth metal is added in a molar ratio, of the metal oxides, which are to be reduced, to the oxide, or carbonate, of the alkaline earth metal, of 1 : 1 to 6:1, the mixture is homogenised, annealed at temperatures of 1,000 to 1,300°C for 6 to 18 hours, cooled and comminuted to a particle size not exceeding 1 mm,

b) calcium, in small pieces, is added in an amount, referred to the oxygen content of the oxides which are to be reduced, equal to 1.2 to 2.0 times the equivalent amount, as well as a booster, the latter in a molar ratio, of the oxides, which are to be reduced, to the booster, of 1 0.001 to 1 0.02, this reaction-bath 1s mixed, the mixture is pressed to produce green compacts, introduced into a reaction crucible and sealed,

c) the reaction crucible is loaded into a reaction furnace, which can be evacuated and heated, the reaction crucible is evacuated to an initial pressure of 10 to 10-¹ Pa, and is heated to a temperature of 1,000 to 1,300°C for a period of 2 to 8 hours, after which it is cooled, and

d) the reaction crucible is removed from the reaction furnace, the reaction product is removed from the reaction crucible and is comminuted to a grain size not exceeding 2 mm, after which the calcium oxide is leached-out by means of a suitable-solvent, in which the alloy powder is insoluble, and the alloy powder, thus obtained, is washed and dried.

2. Process according to Claim 1, characterised in that, in Step a), the oxide, or carbonate, of an alkaline earth metal is added in a molar ratio, of the metal oxides, which are to be reduced, to the oxide, or carbonate, of the alkaline earth metal of 1 1 to 2: 1.

3. Process according to Claim 1 or 2, characterised in that, in Step a), calcium oxide, or calcium carbonate, is used as the oxide, or carbonate, of an alkaline earth metal.

4. Process according to Claim 1, 2 or 3 characterised in that one or several of the process-stages are carried out under a protective gas atmosphere:

in Step a):

Cooling of the annealed oxide mixture, comminution of the annealed oxide mixture,

in Step b):

Mixing of the reaction mixture, pressing the reaction mixture to produce green compacts, introduction of the green compacts into the reaction crucible,

in Step c):

Loading of the reaction crucible into the furnace, which can be heated,

in Step d):

Removal of the reaction crucible from the reaction furnace, removal of the reaction product from the reaction crucible, comminution, leaching, drying of the reaction product.

5. Process according to one or more of the preceding claims, characterised in that one or more of the desired alloying-partners is added to the reaction mixture, in Step b), this alloying- partner being in the form of a metal powder having a particle size not exceeding 40 µm.

6. Process according to one or more of the preceding claims, characterised in that a calcium granulate having an average particle size of 0.5 to 8 mm is used in Step b).

7. Process according to one or more of the preceding claims, characterised in that potassium perchlorate is used as the booster.

8. Process according to Claim 7, characterised in that the potassium which emerges, in gaseous form, from the reaction furnace is absorbed in silica gel.

9. Process according to one or more of the preceding claims, characterised in that the reaction product which is obtained in Step c) is subjected, at a temperature of 600 to 1,000°C, to a vacuum treatment at 10 to 10-² Pa, for a period of 1 to 8 hours.